1. Field of the Invention
The present invention relates to a method for checking the existence of an optical disk, and more specifically, but not by way of limitation, to a method for checking the existence of an optical disk by using the focus error signal or focus OK signal yielded by comparison of a reference level with a beam strength signal.
2. Description of the Related Art
FIG. 1 depicts a general optical disk drive system, comprising an optical pickup 2 for reproducing recorded signals from an optical disk 1, a sled motor 9 for moving the optical pickup 2 along the full length of the disk radius, a spindle motor 10 for rotating the optical disk 1, a drive unit 7 for driving the sled motor 9 and the spindle motor 10, an RF unit 3 for equalizing and shaping the RF signal reproduced from the optical disk 1 by the optical pickup 2, a servo unit 5 for controlling the optical pickup 2 and drive unit 7 using the rotation speed of the optical disk 1 and focus and tracking error signals outputted from the optical pickup 2, a digital signal processing unit 4 for retrieving original digital data from the binary data stream outputted by the RF unit 3, a microcomputer 6 for supervising the operation of the servo unit 5 and digital signal processing unit 4, and a memory 8 for storing data needed for the operation of the microcomputer 6. The focus error (FE) signal generated by the optical pickup 2 will be explained in detail with reference to FIGS. 2A to 2D.
FIG. 2A shows a focus error (FE) signal waveform generated by the optical pickup 2 in the case where no disk is contained in the disk tray of the optical disk drive. Since the incident laser beam is not reflected, the focus error signal is irregular and contaminated by a significant amount of noise, the level of the focus error signal being much lower than a prescribed reference level Refl1.
FIG. 2B shows a focus error signal waveform generated by the optical pickup 2 when an optical disk has been inserted into the disk tray. In this case, the focus error signal is of a sinusoidal waveform and the level is greater than the reference level Ref1a, the amount of noise being relatively small.
FIG. 2C shows a focus error signal waveform generated by the optical pickup 2 in the case where the disk tray contains an optical disk of a low reflection ratio such as a rewritable optical disk. The general shape of the focus error signal is similar to that in FIG. 2B, but the level of the focus error signal is lower because of the low reflection ratio of the optical disk. Therefore, it is likely that the level of the focus error signal does not exceed the reference level Ref1a and the existence of the optical disk is not detected. To solve this problem, the reference level should be lowered enough to detect the optical disk with a low reflection ratio.
If a low reference level Ref1b is employed, an optical disk with a low reflection ratio can be detected as long as the level of the focus error signal exceeds the low reference level Ref1b. In this case, however, it is possible that the level of the focus error signal obtained in the case of no disk goes up the reference level Ref1b as shown in FIG. 2D, which leads to a wrong disk detection result.